Panhandle Pest Update

Grain sorghum fields across the area are flowering or in the grain filling growth stages. These fields are at risk from damaging infesta-tions of head worms (corn ear-worms and fall armyworms). Moth flights for both corn ear-worm and fall armyworm are on the rise. Higher numbers of corn earworm moths have been caught in a light trap at Etter the last two weeks. Also, the number of fall armyworm moths have been very high recently in a pheromone trap at Bushland and have increased in a trap at Etter (See graph). This increases the potential for larvae being found in grain sorghum heads. Fields should be sampled at least weekly during the grain developing stages to determine if infestation levels are at treatable levels.

A beat bucket (white bucket) is a good technique for sampling fields. Sample at least 30 plants from a field and for fields larger than 40 acres take a at least one

sample per acre. Keep a separate count of medium (1/4 inch to 1/2 inch) and large (>1/2 inch) larvae. Then divide each of the two numbers by the total number of heads sampled. This number of medium and large sized larvae per head can be converted to the number of headworms per acre. Larvae smaller than 1/4 inch are not used in making treatment decisions because natural mortal-ity is very high. If most head-worms are this size and the num-ber of medium and large size larvae are not at economic thresh-old, sample the field again in 3 to 4 days.

The economic thresholds for headworms were recently revised by Greg Cronholm and Allen Knutson. Refer to Managing Insect and Mite Pests of Texas Sorghum for a complete explana-tion of headworm thresholds. The threshold is based on cost of control (chemical and application costs combined), the expected market value of the grain, the estimated yield per acre, plant population, and the potential yield loss from feeding larvae. There are two ways to calculate the eco-nomic injury level. Both use the same factors and yield the same results. The first method uses equations to calculate the thresh-old as the number of larvae per head, while the second method determines the number of larvae per acre and is shown in table format in the above guide. Monti Vandiver, Extension Agent-IPM from Parmer and Bailey Counties has written a Microsoft Excel file that will calculate the threshold level as the number of larvae per head. This file is provided as an attachment when e-mailing the newsletter.

The following formulas can be

Sorghum Headworms

Texas AgriLife Extension Service

September 9, 2009 Issue #6

Special points of in-terest:

Sampling for sor-ghum headworms and determining damaging threshold levels.

Cotton Insect

Wheat variety dis-ease and insect rat-ings

Sunflower insect management guide

Upcoming meetings

Ed Bynum, PhD Extension Entomologist 6500 Amarillo Blvd. W.

Amarillo, TX 79106

Phone: 806-677-5600 ext. 612

E-mail

ebynum@ag.tamu.edu

Page 2 Panhandle Pest Update Issue #6

used for calculating threshold levels for medium and large size larvae per head.

If larvae are medium sized (1/4 to 1/2 inch) use the following formula:

For example, if control cost = $9.00/acre (including chemical plus application costs), grain value = $4.50/cwt, and the number of heads per acre = 50,000.

Treatment threshold will be 2 or more

medium size worms per head.

If worms are larger than 1/2 inch in size the following formula should be used to calculate the treatment threshold:

Then if all costs, grain value and number of heads per acre are the same, as previ-ously stated, the calculated treatment threshold for large larvae will be a minimum of 0.4 larvae per head (or at

least 2 larvae per five heads).

Sorghum Midge Greg Cronholm, retired IPM Extension agent for Hale and Swisher counties, but still working, has reported the sorghum midge in high (4-6 per head) to very high numbers (12-18 per head) in some flower-ing fields . This level of midge infesta-tions will cause significant yield loss if not controlled. If you have fields which are still flowering, check them every 2-3 days or until the heads have finished flowering. Information on thresholds and a list of insecticide for midge control can be found in the Texas AgriLife Extension Service publication B-1220, Managing Insect and Mite Pests of Texas Sorghum.

Number of medium-sized larvae per head

Cost of control as $ per acre * 9754

Grain value as $ per cwt * No. heads per

acre * 0.19

=

Number of large sized larvae per

head

Cost of control as $ per acre * 9754

Grain value as $ per cwt * No. heads per

acre

=

The corn earworm and fall armyworm moth activity may also result in bollworm and/or fall armyworm larval infestations in cotton. Dr. David Kerns, Extension cot-ton specialist at the Texas AgriLife Exten-sion Service at Lubbock, provided detailed information about these two insects and when to quit protecting fruit in the Sep-tember 1 issue of Focus on South Plains Agriculture. The following is a summary of Dr. Kerns’s comments. A quality boll requires 750-850 HU to develop. Once a boll has accumulated 450 HU it should be

safe from a bollworm egg lay, but bolls in a high irrigation regime or a shady canopy could be susceptible to damage.

The pyrethoids are the products of choice for bollworms, but good coverage is essen-tial for good control. Pyrethoids are not particularly effective in controlling fall armyworms. So if a large portion of worm population is fall armyworm, a tank mix-ture of an alternative insecticide with a pyrethroid may be warranted. Products such as Belt or Coragen has activity against both fall armyworms and bollworms but

the worms need to ingest these chemicals for best activity.

Cotton Insects

Many of you are making decisions that will influence which variety to chose and your options for minimizing or preventing pos-sible wheat disease infections and insect pest infestations. I am attaching a table as a pdf file that rates wheat varieties accord-ing to their susceptibility or resistance to diseases and pests . This table was com-piled using information from research by Texas AgriLife Research and from the Kansas and the Great Plains 2001 publication

by Steve Watson. Keep in mind there is no one silver bullet or superior wheat variety that is resistant to all diseases and pests. Different varieties will have better resis-tance or tolerance to some diseases and pests than other varieties. For example TAM 112 is a greenbug resistant variety with moderate susceptibility to the Barley Yellow Dwarf Virus that the greenbug vectors. It does express moderate levels of resistance to wheat streak mosaic virus, but

may still become infected under heavy disease pressure. Also, very few varieties have high levels of resistance to any of the diseases. This would mean all varieties could be infected with a disease depending on the severity of that disease.

The varieties in the table are included in the uniform variety trials conducted by Texas AgriLife Research and the Texas AgriLife Extension Service.

Wheat

September 14, 2009, Moore and Sherman counties Cotton Crop Tour, starts at 10:00 am at the Moore County Gin, contact Marcel Fischbacker, CEA at (806) 935-2594 or David Graf, CEA at (806) 366-2081 for information.

September 17, 2009, Claude Grain Sor-ghum turn-row meeting, contact Kyle Stewart, CEA at (806) 226-3021 for infor-mation.

September 22, 2009, 33rd Annual Randall County Ag Show and Crops Tour, contact J.D. Ragland, CEA at (806) 468-5543 for information and to RSVP by Friday Sep-tember 18th.

Agricultural Waste Pesticide Collection Program, 8:00 a.m.—1 p.m. Collection of Pesticides and Used Motor Oil for free at the following locations:

Monday, Sept. 14—Moore Co., Moore County Gin, contact Marcel Fischbacher, CEA, (806) 935-2594

Wednesday, Sept. 16—Deaf Smith Co., Deaf Smith County Bull Barn, contact Rick Auckerman, CEA, (806) 364-3573

Friday, Sept. 18—Hall Co., Hall County Farm Supply, contact Joshua Brooks, CEA, (806) 259-1621.

Upcoming Meetings

Page 3 Panhandle Pest Update Issue #6

Educational programs by the Texas AgriLife Extension Service serve people of all ages regardless of socioeconomic level, race, color, religion, sex, disability or national origin. The information given herein is for educational purposes only. References to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Texas AgriLife Extension Service is implied nor does it imply its approval to the exclusion of other products that also may be suitable.

Late planted sunflowers that are starting to bloom or are blooming can be susceptible to sunflower moth egg lay and may need to be protected. We have just completed updating our guide, Managing Insect Pests of Texas E-579.

Research has shown that insecticide should be applied when 15 to 25 percent of plants are blooming and sunflower moths are found in the field. Unfortunately, bloom-ing can progress so rapidly that by the time the producer gets spray equipment or an airplane into the field, it may be too late for an application to be completely effec-tive. Follow these suggestions for effec-tive sunflower moth control.

At least 2 weeks before spraying, se-lect and get a commitment from a custom applicator to be ready to spray; also decide which chemicals you will use so the applicator will have them on hand.

Be ready to begin scouting as soon as you see the first blooming head in the field (late R4 stage). If you are a first-time grower, get assistance from those experienced in scouting for sunflower moth.

Besides the initial application, one to two additional insecticide applications at 5-day intervals may be needed when sunflower moth populations are moderate to heavy and moths are still active. In more north-ern states, pheromone trap sampling from growth stages R3 to R5.1 indicate that fields are at a high risk when more than four moths are captured per trap per night. However, treatment decisions should be made on the basis of scouting for adults at the time of bloom. Trap captures of fewer than four per night do not mean a field is safe from economic damage.

Sunflower Insects